The present invention relates to a magnetic apparatus for detecting a position of a vehicle that calculates a lateral deviating distance of a vehicle from the centerline on the road by detecting a magnetic field generated from magnetic markers located on the centerline of the road.
An automatic driving system has been researched by various approaches. The principles for these approaches are to detect a cable with current by a pickup coil, to analyze a figure by camera, to use radiowaves, to use an ultrasonic device, to detect magnetic tape by a magnetic sensor and so on. However, these methods, except magnetic methods, are difficult to apply to vehicles running on the road in bad weather (rain, snow, mist and so on). The magnetic methods in which linearly arrayed sensors detect a magnetic line is usually adopted to an automatic driving system used in a plant, but it is difficult for arrayed sensors to apply to guiding vehicles on roads because of high speed and vertical oscillation.
U.S. Pat. No. 5,347,456 discloses a magnetic guiding method for vehicles. According to this method, a magnetic sensor set on a vehicle detects both vertical component and transverse component of a magnetic field and then a lateral deviating distance is calculated from this data accompanied with the correction of the vertical oscillation of the vehicle.
However, the vertical component of the magnetic field considerably decreases when the magnetic sensor is set at a height of more than about 20 cm to 25 cm. So the detectable range of the lateral deviating distance is very narrow at about 20 cm to 25 cm. Therefore it is noted that the magnetic guiding system does not operate when a vehicle does not enter into the area within about 20 cm to 25 cm from the center of the road.
As usual a vehicle is correctly guided within about 20 cm to 25 cm from the centerline of the road. But the problem remains that the vehicle deviates from the centerline over 25 cm and becomes out of control when the vehicle is running through bridges or tunnels because they are made of reinforced concrete that generate the magnetic field. The external magnetic field is locally as strong as the magnetic field generated from magnetic markers. Here the word xe2x80x98externalxe2x80x99 means xe2x80x98except things by magnetic markersxe2x80x99.
For example, the vehicle is running 20 cm distant from the centerline to the right. In this situation the magnetic sensor of the vehicle detects the right directed component of the magnetic field generated from magnetic markers located in the centerline. If the left directed component of the external magnetic field is larger than the right directed component of the magnetic field generated from markers, the computer misjudges that the vehicle is running on the left side of the lane. From this misjudgment the computer guides the vehicle toward the right.
The magnetic markers are set along the centerline at the interval of 2 m. However there is the case that the vehicle deviates at distance of about 25 cm from the centerline while it goes about 1 m. In this undesirable case, the guiding system easily becomes out of control. Here the maximum of steering angle of 5 degrees, the vehicle width of 1.7 m and the lane width of 3.5 m are assumed.
The maximum of the distance between the magnetic marker and the magnetic sensor is 0.9 m in these above assumptions. If the magnetic guiding system has the detectable range of about 1 m, the magnetic sensor can detect the magnetic marker always when the vehicle is on the lane. That means that the system certainly and correctly guides the vehicle toward the centerline. But the above-mentioned system has the detectable range of only about 25 cm. The range is insufficient.
Moreover in running on a curve, a lateral deviating distance varies at the point of every magnetic marker. It is necessary to detect the deviating distance from the centerline while a vehicle goes 2 m. And the above-mentioned system uses so complex method to calculate the position of vehicle that the system needs long time to identify the position of the vehicle.
It is desirable that the interval of magnetic markers is shorter than 2 m. In order to solve this problem, the new magnetic guiding system is expected. It must be able to easily detect the lateral deviating distance with high accuracy in spite of the interval of 2 m for markers.
This invention is made in order to solve the above problem. The subject of this invention is to provide the magnetic apparatus for detecting position of vehicle that can detect the lateral deviating distance from centerline with wide detectable range, high accuracy and short response time.
Disclosure of the Invention
To solve this problem, the inventors found out a new method to enhance the ability of the sensor for keeping a position of a vehicle on the centerline and to extend the detectable range of the sensor for the lateral deviating distance from 25 cm to 1 m. The detectable range becomes 4 times larger. The method is characterized by detecting the longitudinal component of the magnetic field. The longitudinal component means along the lane. Moreover it is favorable to detect three components of the magnetic field. Three components are the longitudinal component, the vertical component and the transverse component. In this method, when the lateral deviating distance between the sensor and the marker becomes over 25 cm because of the misjudgment brought by external magnetic field, the system certainly and correctly guides the vehicle toward the centerline and recovers the vehicle at the center position of the lane.
The Following are Details of this Invention.
A magnetic apparatus for detecting position of the vehicle detects a lateral deviating distance between the vehicle and the centerline (correctly between the magnetic sensor and magnetic markers) using the measured value for the longitudinal component of the magnetic field.
As after mentioned the appreciative magnetic apparatus for detecting position of the vehicle comes true by this system. This apparatus can detect accurately the lateral deviating distance with wide detectable range compared to the conventional apparatus that detects not the longitudinal component but the other components of the magnetic field.
The magnetic apparatus for detecting a position of a vehicle is characterized by detecting the lateral deviating distance using the largest variation of the longitudinal component of the magnetic field.
Here, the largest variation is the difference between the maximum output signal and the minimum output signal of the magnetic sensor that detects the longitudinal component of the magnetic field. The largest variation is dependent on the lateral deviating distance.
This method makes it possible to detect accurately the lateral deviating distance.
The magnetic apparatus for detecting a position of a vehicle is characterized by detecting the lateral deviating distance using Lx. Here, Lx is defined as the distance obtained by multiplying a vehicle""s speed together with the period from the minus peak time to the plus peak time of a Bx output signal. The plus or minus peak time means the time to get the maximum or minimum output signal of the magnetic sensor respectively. Lx is dependent on the lateral deviating distance. This method makes it possible to detect accurately the lateral deviating distance.
The magnetic apparatus for detecting a position of a vehicle is characterized by detecting the lateral deviating distance using three components of the magnetic field. The above three components are detected by the vertical magnetic sensor, the transverse magnetic sensor and the longitudinal magnetic sensor. This method makes it possible to detect more accurately the lateral deviating distance, when the lateral deviating distance is small. In other words, the vertical magnetic sensor detects the component normal to the lane plane, and the transverse magnetic sensor detects the component parallel to right-and-left direction of the vehicle.
The magnetic apparatus for detecting a position of a vehicle is characterized by detecting the lateral deviating distance using the vertical and transverse components measured at the moment when the longitudinal component reverses from plus to minus. This method makes it possible to detect accurately the lateral deviating distance.
The magnetic apparatus for detecting a position of a vehicle is characterized by detecting the lateral deviating distance using the peak values or the average values of the vertical component and the transverse component. Here, the average value is defined as the average of the peak values and the values at the moment when the longitudinal component reverses from plus to minus. This method makes it possible to detect accurately the lateral deviating distance.
The magnetic apparatus for detecting a position of a vehicle is characterized by detecting the lateral deviating distance using three different combinations of three components according to the lateral deviating distance.
The magnetic apparatus for detecting position of vehicle provided in the claim 7 comparing with that of claim 4 is characterized by detecting the lateral deviating distance using different three combinations of three components according to the lateral deviating distance.
When the lateral deviating distance is large, both the longitudinal component and the vertical component are used. The longitudinal component provides the lateral deviating distance and the transverse component shows whether the vehicle is running on the left side or on the right side.
Next when the lateral deviating distance is medium, both the longitudinal component and the vertical component are used in the similar manner, accompanying with the correction of the vertical oscillation.
And when the lateral deviating distance is small, both the transverse component and the vertical component are used. The lateral deviating distance is obtained by both components accompanied with the correction of the vertical oscillation and the transverse component shows whether the vehicle is running on the left side or on the right side.
This method makes it possible to detect accurately the lateral deviating distance with wide detectable range. Especially when the lateral deviating distance is large, this method can enhance the accuracy of detection.
The magnetic apparatus for detecting a position of a vehicle is characterized by using frequency bands of the signal from magnetic markers eliminating other frequency bands from noises. The accuracy of detection can be enhanced.
The magnetic apparatus for detecting a position of a vehicle is characterized by calculating the longitudinal position of a magnetic marker from the output signal of the longitudinal magnetic sensor. This method makes it possible to detect accurately the longitudinal position of a magnetic marker.
The magnetic apparatus for detecting a position of a vehicle is characterized by calculating the longitudinal position of a magnetic marker from three detected peak values of three components, that is, a longitudinal one, a transverse one and a vertical one.
Then the apparatus calculates a midpoint between a current marker passing at the moment and a next marker with calculated positions of some previous markers. From a magnitude of the magnetic field on this midpoint, the apparatus calculates a level of the background magnetic field except the magnetic field from magnetic markers (the signal magnetic field), especially detects a level of the external magnetic field with a long period. Then the apparatus derives the signal magnetic field from the values detected by the magnetic sensor by subtracting this background magnetic field.
The magnetic apparatus for detecting a position of a vehicle is characterized by the method eliminating a noise generated from the short period external magnetic field. The type of the noise can be eliminated by using both values of the lateral deviating distance derived from the current marker passing at this time and the average distance derived from some continual previous magnetic markers. This method can enhance the accuracy of detection.
The magnetic apparatus for detecting a position of a vehicle is characterized by equipping the means to detect information about the road with various configurations of magnetic markers. This method can make the apparatus multifunctional. For example, in a dense fog the apparatus informs a driver about the bumpiness, curve, and incline rate in a road.
The magnetic apparatus for detecting a position of a vehicle is characterized by equipping the means to calculate a velocity of a vehicle with the time to pass the space between adjacent magnetic markers. This method makes it possible to detect a velocity of a vehicle without the addition of the speed sensor.
The magnetic apparatus for detecting a position of a vehicle is characterized by steering control with the derived lateral deviating distance. This method can make the automatic driving safe and comfortable.
(The Account of the Principle to Calculate the Lateral Deviating Distances by Using the Three-dimensional Magnetic Sensor)
The Detecting Method (1)
The method to detect a small lateral deviating distance.
The method uses the vertical component of the magnetic field, Bz, when a lateral deviating distance is small (for example within 25 cm ). Because the output of Bz is much larger than that of the other two components near the center of the magnetic marker, and sharply decrease with increase of a lateral deviating distance. The method makes it possible to measure a lateral deviating distance with accuracy of about 2 cm. Besides the transverse component of the magnetic field, By, shows whether a vehicle is running on the left side or right side of a lane. Because the By output voltage of the magnetic sensor on left side from a magnetic marker shows the different sign from that of the magnetic sensor on right side from a magnetic marker.
When it is necessary to correct influence of the height of the magnetic sensor, the map shown in FIG. 6 is used for calculating a lateral deviating distance. This map is composed of the vertical component maximum of the magnetic field (which is called as Bzmax) and the transverse component maximum of the magnetic field (which is called as Bymax) using two parameters, the height of the magnetic sensor and the lateral deviating distance.
Besides in any lateral deviating distance, the maximum of Bz is obtained at the moment when the magnetic sensor passes over or abeam the magnetic marker. Similarly, the maximum of By is obtained at the moment when the magnetic sensor is over or abeam the magnetic marker. As mentioned above, Bz is the vertical component of the magnetic field and By is the transverse component of the magnetic field.
The lateral deviating distance can be calculated directly by using the map shown in FIG. 6. The lateral deviating distance can be calculated also by using one simple equation that is derived from the one-to-one relation between a lateral deviating distance and a ratio of Bzmax to Bymax shown in FIG. 7.
The Detecting Method (2)
The method to detect a medium lateral deviating distance.
The method uses the transverse component of the magnetic field, By, and the longitudinal component of the magnetic field, Bx when a lateral deviating distance is medium about from 25 cm to 50 cm.
The output signal of the transverse component of the magnetic field, By, has a one-to-one correspondence to a lateral deviating distance in the case that a lateral deviating distance is above 10 cm. Moreover the transverse component of the magnetic field, By, spreads far and wide. To use the transverse component makes it possible to measure a lateral deviating distance with accuracy of about 4 cm. However, it is difficult to distinguish the transverse component of the magnetic field generated from the magnetic marker from the transverse component of the external magnetic field. The reason is that the latter noise interferes with the former signal, and the sign of By output signal keeps before and after a vehicle pass through a magnetic marker.
On the other hand, although the longitudinal component of the magnetic field, Bx also spreads far and wide, the sign of output signal changes before and after a vehicle pass through a magnetic marker. So it is easy to distinguish the longitudinal component of the magnetic field of magnetic markers from the longitudinal component of the external magnetic field. Therefore it is suitable to combine Bx and By for measuring a lateral deviating distance from 25 cm to 50 cm.
When it is necessary to remove affect of a height of the magnetic sensor, the map shown in FIG. 8 is used. The coordinates of the points in the map for Bxmax and Bymax show both values of a height of the magnetic sensor and a lateral deviating distance. Using the map, a lateral deviating distance is calculated with correction of the obtained height of the magnetic sensor. Besides a lateral deviating distance can be obtained directly from the map shown in FIG. 8 and can be calculated by using one simple equation that is derived from the one-to-one relation between a lateral deviating distance and a ratio of Bxmax to Bymax shown in FIG. 9.
The Detecting Method (3)
The method to detect a large lateral deviating distance.
The method uses the transverse component of the magnetic field, By, and the longitudinal component of the magnetic field, Bx in the case of a large lateral deviating distance from 50 cm to 100 cm. The method can obtain accurately a lateral deviating distance by calculating the longitudinal distance between the Bx maximum point and the Bx minimum point as shown in FIG. 10 and FIG. 24. Here the Bx maximum point and Bx minimum point mean the points at which Bx show maximum and minimum values respectively. In this case, whether the vehicle is running on left or right side from the centerline of the road is judged from the sign of the transverse component of the magnetic field, By. This method can neglect the influence of the height of the magnetic sensor. Speaking repeatedly, Bx is the transverse component of the magnetic field, and By is the transverse component of the magnetic field. By the way, FIG. 10 is obtained from computer simulation and FIG. 24 is obtained from an experiment. The assumption for this simulation and experiment is that the magnetic marker has the diameter of 100 mm and the thickness of 5 mm. And it is set over 250 mm from the upper surface of the magnetic marker.
The Detecting Method (4)
Another method to detect a large lateral deviating distance.
The method can get a lateral deviating distance by using the map (refer to FIG. 25) that shows the relation between calculated Bxmax and a lateral deviating distance in a large lateral deviating distance from 30xcx9c40 cm to 100 cm. Here Bxmax is defined as the gap between the maximum value of Bx and the minimum value of Bx. As shown in FIG. 25, Bxmax is only a little dependent on a height of the magnetic sensor in this lateral deviating distance. Therefore a lateral deviating distance is calculated accurately and quickly without correcting the affect of a height of the magnetic sensor. By the way, in the same manner of method (3), whether the vehicle is running on left or right side from the centerline of the road is judged from the sign of the transverse component of the magnetic field, By.
When a lateral deviating distance is large, the method (4) can detect a lateral deviating distance by using Bxmax more accurately compared to the method (3) to detect it by using the longitudinal distance between the Bx maximum point and the Bx shows minimum point.
However, the output signal of Bxmax is remarkably dependent on the height of the magnetic sensor when a lateral deviating distance is within 30 cm, as shown in FIG. 25. Therefore in this area, the method (4) to detect a lateral deviating distance by using Bxmax requires the correction to remove the affect of the height of the magnetic sensor. So it is possible to select a suitable method among method (1)NHxcx9cmethod (3) for detecting a not large lateral deviating distance and adopt method (4) for detecting a large lateral deviating distance.
Another Detecting Method (5)
Moreover it is possible to calculate a lateral deviating distance from the transverse component of the magnetic field By roughly. In this case, the influence of the vertical oscillation of the magnetic sensor is neglected. It is possible to select Bx or By for detecting a lateral deviating distance according to circumstances. Moreover, it is possible to use the average value of two detected lateral deviating distances. One is detected by using Bx and the other is detected by using By.
However, it is desirable to use Bxmax not By for detecting a lateral deviating distance. Here Bxmax is the gap between the maximum value of Bx and the minimum value of Bx. The reason is that the magnetic field generated from magnetic marker overlaps with the external magnetic field and using Bx can make it easy to separate the former from the latter. In other words, it is difficult to separate the former from the latter by using By.
(The Account of the Method to Guide a Vehicle Toward the Centerline of the Road)
The following is the explanation of the method for guiding a vehicle toward the centerline.
As mentioned above, the conventional system does not operate when a vehicle does not enter into the area within 25 cm from the centerline. On the other hand, the present method using a variation of Bx can guide a vehicle from any position.
Besides, there are three methods to detect a lateral deviating distance. One only uses Bx. Another uses both Bx and By. The other uses both Bz and By. Selecting a suitable method among these three methods makes it possible to detect accurately a lateral deviating distance, under every condition that a lateral deviating distance is small, medium and large.
For example, a lateral deviating distance from the centerline is 50xcx9c100 cm when a vehicle enters to the magnetic guiding lane. So a lateral deviating distance is detected with the method (3) using Bx and By.
Next, when a lateral deviating distance decreases due to guiding with method (3), a lateral deviating distance is detected with the method (2) using Bx and By. And a vehicle is guided toward the centerline according to this detected lateral deviating distance.
Furthermore, when a lateral deviating distance more decreases, a lateral deviating distance is detected accurately with the method (1) using Bx, By and Bz.
Besides, even if a lateral deviating distance becomes over 25 cm, above-mentioned methods can guide a vehicle toward the centerline before a vehicle drive out of the road.